This invention relates to a copying apparatus for transcribing the impression of an original sheet on a copy sheet, and more particularly to a copying apparatus provided with an original density-detecting device for sensing the average original density of an impression indicated on an original sheet.
A recent copying apparatus is constructed by installing a light intensity detector for sensing an intensity of light rays reflected from an original sheet placed on an original sheet-mounting section of an original sheet holder in an optical path of an exposure optical system. The light intensity detector is intended to sense the average original density of an impression indicated on the original sheet. The copying apparatus automatically controls a copy density of an impression to be copied from the result of the detection for each copying operation in order to provide a distinct copied impression.
The U.S. Pat. No. 4,017,180 already discloses the proper position of a light intensity detector included in an exposure optical system installed in a copying apparatus. According to this U.S. patent, the light intensity detector takes such a position at such a light-receiving angle as allows for the reception of light reflections from the whole surface of an original sheet-mounting section. If, therefore, the original sheet happens to be smaller than the original sheet holder and have a widely different density than an original sheet keep cover or if a book containing an original sheet to be copied has too great a thickness to have its peripheral edge fully covered with the original sheet keep cover, then the drawback arises that the result of detecting the light intensity by the detector does not fully correspond to the density of the impression indicated on the original sheet.